/Engine/Source/Runtime/NavigationSystem/Public/NavMesh/NavMeshPath.h
It's only const to be callable in const environment. It's not supposed to be called directly externally anyway, just as part of retrieving corridor on demand or generating it in internal processes. It fills a mutable array.
const [TArray](API\Runtime\Core\Containers\TArray)< [FNavigationPortalEdge](API\Runtime\Engine\AI\Navigation\FNavigationPortalEdge) > & GeneratePathCorridorEdges() const